Williams ran the Symbian Series 60 platform for Nokia between 2006 and 2009, then was the executive director Symbian Foundation for a while until Nokia brought the operating system back in house in 2010.

In an interview with CNET UK, Williams has almost nothing nice to say about Nokia's new boss, who joined from Microsoft about a year and a half ago. Williams says that Elop has no roadmap for the company, is losing top talent and replacing it with junior execs from Microsoft, and runs the company more like a penny-pinching CFO than a visionary CEO.

But his worst criticism is that Elop didn't milk Nokia's main cash cow, Symbian, for long enough, and instead made a hasty all-or-nothing bet on Windows Phone. He told CNET:

"Symbian is shipping on around 20 million new units a quarter as of today. When I was at the company it was responsible for seven of 10 of Nokia's highest gross margin products....When I was at Nokia and we shipped a Symbian product and it was bad, in its worst incarnation we knew that if we just flipped the switch, we could move 2.5 to three million units -- overnight, no matter how bad the product."

He continued:

"And now look at it -- they flipped the switch and oh, 200,000 [Windows Phone] units out of the gate. Huh? Only selling in the US, under AT&T's moniker. If you can't flip the switch like that, Nokia's dead and devalued."

While old-guard companies like Microsoft and Oracle are often criticized for moving too slowly against long-term threats, Elop looked at the situation and make a dramatic leap, and he's getting slammed for it.